[Equest-users] Central GSHP system pump energy

David Reddy david.j.reddy1 at gmail.com
Wed Jun 2 23:20:10 PDT 2010


Is your lake/well  loop sizing option set to "Secondary" or "Primary".  
I don't actually remember if this matters for lake/well loops, but if 
you input a capacity for the heat pump and set to "Primary", the program 
should size the flow based on the heat pump's capacity and the dT across 
the condenser.  You can also adjust the loop size (flow) with the 
LOOP-SIZING-RATIO

A few other things to consider:

1) If you have a heat exchanger with the ground loop, it is probably 
best to account for the approach of the HX with the lake/well supply 
temp.  The default temp of the loop is the ground temp included in the 
weather file, which varies on a monthly basis rather than constant all 
year.  You can create your own schedule based on the weather file temps 
that includes an approximation of the HX approach...
2) Is your HP really a loop to loop?  I have seen projects that attempt 
to use this type of chiller when really it is a series of water-to-water 
HP manifolded to provide simultaneous hot and chilled water.  These are 
very different systems...
2) Regardless, I would recommend getting performance data for your heat 
pump to generate your own performance curves, as the default curves are 
quite dated.
3) Once you have done step 2, check hourly reports to see if can compare 
some part load conditions in the simulation result with those reported 
by the manufacturer.  This can be difficult, but is about the best way I 
can think of to know if the simulation of this type of equipment is 
reasonable.

David Reddy

360 Analytics
Building Energy Analysis Consultants
mail:	12354 16th Ave NE, Seattle, WA 98125
phone:	206.406.9856
email:	david at 360-Analytics.com


On 6/2/2010 3:01 PM, jacob goodman wrote:
> I'm working on a system that uses an open loop ground well tied to a 
> loop-to-loop heat pump (see screen shot below) with Lake/Well loop 
> type and GSX type.  This heat pump serves hot and cold  water loops 
> tied to fan coils. The "ground temp" is water being pulled out of a 
> deep aquifer and set to 50 deg year round.
>
> I have gotten the model to run without errors, but I am getting very 
> high pump energy use from the ground loop. The head and pump sizing 
> seem high but reasonable, but the flow seems way too high. I'm getting 
> 540 gpm peak and was expecting closer to 300 gpm.  This results in 18% 
> of electricity use going to pumps, 17% going to heating and cooling 
> combined.
>
> Any suggestions?
>
>
>
> Jacob Goodman , LEED AP, Green Building Specialist
> v:509.280.7051  i:www.lseng.com <http://www.lseng.com>
> L&S  Engineering Associates, Inc.
> 'High Performance Design'
>
>
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